docs: def enrich_proteins_with_rnas(graph):
      """Add the corresponding RNA node for each protein node and connect them with a translation edge.
  
      :param pybel.BELGraph graph: A BEL graph
      """
      for protein_node in list(graph):
          if not isinstance(protein_node, Protein):
              continue
  
          if protein_node.variants:
              continue
  
          rna_node = protein_node.get_rna()
          graph.add_translation(rna_node, protein_node)